In this application we propose light microscopic (LM) and electron microscopic (EM) studies of autroadiographically, immunocytochemically, or morphologically distinct neuronal classes in the cochlear nucleus (CN) and superior olivary complex (SOC) of the gerbil to map the presence of the putative neurotransmitters GABA and glycine (GLY) in identified classes of neurons, and to provide a quantitative description of the distribution of the different synaptic terminal populations incident on their surfaces. This work builds upon our previous studies in which characteristics for distinguishing individual neuronal populations were identified. It will utilize newly developed light and electron microscopic postembedding immunocytochemical procedures to map to the distribution of immunoreactivity to newly developed anti-GABA (A/GABA) and/or anti-GLY (A/GLY) antibodies in 1) identified classes of neuronal somata in the CN and SOC, 2) synaptic terminals on identified neuronal somata in the CN and SOC, 3) synaptic terminals and apposed neural elements on somata, dendrites, axons and collaterals of medial and lateral olivocochlear neurons (MOC & LOC) selectively labeled with tritiated nipecotic or d- aspartic acid retrogradely transported from the cochlea. This information is necessary, but not sufficient, to identify GABA or GLY as putative transmitters of labeled populations. Additional chemical markers will be sought to identify other functionally distingishable populations of neruons and termainals and to aid in identifying the targets of individual neuronal classes. To assess the continued suitability of the gerbil as a model for studies of the auditory system, we will make quantitative measurements of cell size, cell number and cell types in the posterovental cochlear nucleus (PVCN) where the presence of a spongiform encophalopathy has recently been described. We will determine whether any population of neuons (of glia are selectively effected. Changes will be assessed as functions of age and extent of lesion.